Osmosis and diffusion

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Labbie
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Re: Osmosis and diffusion

Post by Labbie »

Do a search for the little plastic bags that are ade just for the experiment. They really are very very good.
The starch solution is just put in freezer bags for the junior school as it is much more cost effective and works just as well. taken from fibreweb post. :popcorn: :crazy: :coffee:

Also see thread of Iodine for a good read.
Regards Labbie

Lab Manager/Lab Tech, mind reading etc etc
Now retired :wub:
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Ian
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Re: Osmosis and diffusion

Post by Ian »

We did this one last week, with 1% starch, just as you have illustrated. One set up worked, in that the starch went black, and the other 6 or so did not work!!! (go figure!) In all of them, the level of water in the thistle funnel went DOWN, Not UP. I am beginning to believe that Science is NOT "Cause and Effect", and reproducible experiments after all, but actually voodoo, and magic with a mind of its own!!! (and sent to torment me!)
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Rita
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Re: Osmosis and diffusion

Post by Rita »

Hi All

We did the iodine and starch solution for this prac without measuring side of things. The teacher also asked for sucrose and glucose both 1M. Has anyone used these as well for diffusion prac? Seems a strong concentration....1M sucrose is 34.23%.
Thanks for your thoughts.
Rita
Merilyn1
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Re: Osmosis and diffusion

Post by Merilyn1 »

Ian wrote:We did this one last week, with 1% starch, just as you have illustrated. One set up worked, in that the starch went black, and the other 6 or so did not work!!! (go figure!) In all of them, the level of water in the thistle funnel went DOWN, Not UP. I am beginning to believe that Science is NOT "Cause and Effect", and reproducible experiments after all, but actually voodoo, and magic with a mind of its own!!! (and sent to torment me!)
:cheesy:
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melsid
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Re: Osmosis and diffusion

Post by melsid »

My lot order a saturated sucrose solution, but I've been giving them around 5 - 10% or so and it works just fine.
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Ian
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Re: Osmosis and diffusion

Post by Ian »

Rita wrote:Hi All

We did the iodine and starch solution for this prac without measuring side of things. The teacher also asked for sucrose and glucose both 1M. Has anyone used these as well for diffusion prac? Seems a strong concentration....1M sucrose is 34.23%.
Thanks for your thoughts.
Rita
I think sometimes, teachers say "1 molar" when what they mean is just "sort of standard concentration, but not too strong" I once had a teacher ask me for a 1M concentration of Calcium Carbonate!!!! (I stirred that for a long time before twigging that CaCO3 is insoluble! And she wasn't even pranking me!!) :giggle: :crazy:
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Ian
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Re: Osmosis and diffusion

Post by Ian »

melsid wrote:My lot order a saturated sucrose solution, but I've been giving them around 5 - 10% or so and it works just fine.
Saturated Sucrose solution? Is that "Stick jaw" toffee or "Brittle" toffee? Sounds yummy either way! \:D/
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Kathryn
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Re: Osmosis and diffusion

Post by Kathryn »

Good morning. My teacher has always asked for litres of iodine solution to pour straight into the beakers containing the starch dialysis tubing. Of course when I make up the iodine as per the recipe it is far too dark so then have to dilute. Should she actually just be adding a few drops of iodine from our usual 0.1M iodine dropper bottles to water filled beakers?
thanks :)
bigmack
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Re: Osmosis and diffusion

Post by bigmack »

Droppers won't do it .....its just not strong enough .

I give them a small stock solution of Iodine that is 10x strength ( I dilute it down for droppers )

They just carefully add it to the water in the beaker , gas jar what ever , until it is a pale brown colour . ....works everytime
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KassH
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Re: Osmosis and diffusion

Post by KassH »

Hi, I need some help. I've not prepared this prac before and I have no iodine solution made up. Do you use potassium iodine or straight iodine? And how concentrate?
I started making up a potassium iodine solution but it's clear??
labbassistant
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Re: Osmosis and diffusion

Post by labbassistant »

We use Aqueous iodine solution, I've attached a photo for the recipe.
And also a 1% or 1.5 % starch solution
Hope this helps
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labbassistant
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Re: Osmosis and diffusion

Post by labbassistant »

Sorry, I should've asked before. Is this with the dialysis tubing diffusion prac?
That's what we use for that diffusion prac
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Ian
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Re: Osmosis and diffusion

Post by Ian »

Teachers will often ask for Potassium Iodide solution (KI) when what they really mean is Iodine Solution (I/KI) or sometimes called Lugol's Iodine Solution. Yes, KI is a perfectly clear liquid and will NOT do what they want (ie, turn starch black/purple) but it is necessary to make the iodine dissolve in water. The recipe that Labassistant has given you (from the book, "The Laboratory") is a good one. There are a couple of similar but equally good recipes in that book.
They do suggest that the I/KI solution be made up 24 hours in advance.
Actually, an interesting experiment you can do, if you are not totally run off your feet, like most of us are, most of the time) is to add a few grains of iodine to a beaker of water. No matter how you stir it, it will just sit there and not dissolve. Then add a couple of grains of KI to the beaker. Immediately the I will start dissolving into the water in brown swirls! (maybe I am a nerd, but I found it interesting!)
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KassH
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Re: Osmosis and diffusion

Post by KassH »

Thank you labbassistant and Ian. It is for the dialysis tubing prac.
I used the potassium iodine solution I had made up (with 16.6g KI) and added the 3g of iodine. It's now brown so guessing it's good to go. The extra 1.6g of KI shouldn't matter, right? Don't have 24hrs for it to sit but they will have to make do with that.
labbassistant
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Re: Osmosis and diffusion

Post by labbassistant »

If everything is dissolved then there shouldn't be a problem.
Happy to help!
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